A variety of devices have an articulating distal end which is controlled by a mechanism disposed along its proximal end. This allows remote articulation of the distal end and is particularly useful for situations wherein the distal end is not accessible. In medical devices, a variety of catheters and surgical instruments have elongate distal ends which are introducible into the body for various treatment procedures. Typically, the proximal end includes a handle which remains outside of the body and includes mechanisms for controlling and articulating the distal end which is remote and inaccessible.
FIG. 1 illustrates an example catheter 10 comprising an elongate shaft 12 and handle 16. Here, the elongate shaft 12 is articulatable along its distal end 14 for steering and maneuvering remotely. In this example, such articulation is achieved with the use of a pull ring 20 positioned around the elongate shaft 12 near the distal end 14 which is connected to a pull wire 22 which extends along the shaft 12 toward a proximal end 18. In this example, the pull wire 22 is connected to a rotating cuff 24 along the handle 16, wherein rotation of the cuff 24 applies pulling force to the pull wire 22 which causes bending of the distal end 14 as indicated by the dashed line image. In this example, rotation of the cuff 24 in the opposite direction releases the pulling force and allows the distal end 14 to recoil to its original position. It may be appreciated that a pull ring 20 may have multiple pull wires 22 for articulation in various directions, and/or a catheter 10 may have multiple pull rings 20 for various types of articulation.
Typically, pull rings 20 and their attached pull wires 22 are comprised of stainless steel due to the large forces applied for articulation. In some instances, a pull ring 20 with a 0.010 inch pull wire 22 having an ultimate tensile strength of 27 lbf will have a design requirement of 15-20 lbf. Or, a pull ring 20 with a 0.015 inch pull wire 22 having an ultimate tensile strength of 62 lbf may have a design requirement of 40-50 lbf.
Typically, the pull ring 20 is cut from full-hard stainless steel tubing and includes a slot 30 which is laser cut into the wall of the tubing for insertion of the pull wire 22, as illustrated in FIG. 2. In this example, the pull ring 20 is cut from tubing having an outer diameter of 0.230 inches and an inner diameter of 0.200 inches, thus having a wall thickness of 0.015 inches. The pull wire 22 is then welded to the wall of the tubing to fix the pull wire 22 in place. Such welding is usually low energy so that the pull wire 22 is not significantly damaged. In this example, the pull wire 22 has a diameter of 0.015 inches. In most instances, the pull ring 20 is has a length that is as short as practical to minimize stiffness of the catheter shaft 12 when placed therearound, allowing the catheter to easily track over a guidewire or pass through an introducer. In this example, the pull ring 20 has a length of 0.150 inches. In addition, the slot 30 is typically cut as long as practical to maximize the weld length (allowing the use of low energy) so that the pull wire 22 does not fail in shear. This combination of design features, particularly low energy welds over a long distance, maximizes the ultimate tensile strength of the weld so as to approach the ultimate tensile strength of the wire.
Since the distal end 14 of the catheter 10 is within the patient during use, the user is unable to visualize the articulation of the distal end 14. In most situations, such visualization is achieved by the use of fluoroscopy. In some instances, one or more marker bands are positioned along the catheter shaft 12 wherein the marker bands are comprised of a radiopaque material, such as gold or platinum, which is visible under fluoroscopy. However, such bands add additional cost, labor and dimension to the catheter 10. In some instances, pull rings 20 may be used to assist in visualization of the articulating end, however thin bands of stainless steel are difficult to easily identify under fluoroscopy, particularly amid other devices used in conjunction with the articulating catheter and other hardware that may have been previously installed in the patient.
Consequently, pull rings 20 have been modified to increase their visibility under fluoroscopy. For example, stainless steel pull rings 20 have been plated in gold to increase their visibility. Such plating is typically 0.002 or 0.003 inches thick. This significantly increases the wall thickness of the pull ring 20, such as adding dimension to the inner diameter and outer diameter of the pull ring 20. Thus, the catheter 10 will have an overall larger French size and a smaller lumen through which to pass another device, both of which are contrary to optimization of the catheter 10.
In other instances, platinum marker bands have been positioned adjacent to or on top of stainless steel pull rings 20. Placing the marker band adjacent to the pull ring 20 creates a long region of stiffness along the catheter shaft 12, reducing the flexibility of the shaft 12. Placing the marker band on top of the pull ring 20 increases the diameter of the pull ring 20, which as mentioned increases the overall French size of the device which is disadvantageous.
In yet other instances, platinum marker bands have been attempted to be used as pull rings 20, however platinum is relatively soft even with the addition of elements such as tungsten or iridium. Stainless steel pull wires 22 welded to platinum marker bands will not produce the desired ultimate tensile strength for most design applications where pull rings 20 are used for articulation, leading to breakage of the bond and/or damage to the marker band, pull wire, or catheter.
Therefore, improved methods and devices are desired for visualization of remotely articulating portions of devices or instruments without compromising design features such as profile, inner diameter, outer diameter, flexibility or strength. At least some of these objectives are met by the present invention.